CVE-2026-84640

One byte overflow read in mail parser

State: Published
Severity: 7.5 High
Published: Sep 1, 2026
Updated: Sep 2, 2026
Reserved: Sep 1, 2026

Description

A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

Scores

CVSS	Score	Vector	Source
3.1	7.5 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N	CISA-ADP

Weaknesses

CWE-126 Buffer Over-read

Affected Products

Product	Versions
ThunderbirdMozilla	140.15 through 140.Not affected 153.2 through 153.Not affected 155 and laterNot affected

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2063964
https://www.mozilla.org/security/advisories/mfsa2026-86/
https://www.mozilla.org/security/advisories/mfsa2026-87/
https://www.mozilla.org/security/advisories/mfsa2026-88/

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